scholarly journals Geodesic motion of S2 and G2 as a test of the fermionic dark matter nature of our Galactic core

2020 ◽  
Vol 641 ◽  
pp. A34 ◽  
Author(s):  
E. A. Becerra-Vergara ◽  
C. R. Argüelles ◽  
A. Krut ◽  
J. A. Rueda ◽  
R. Ruffini
Keyword(s):  
Dark Matter ◽  
Radial Velocity ◽  
Drag Force ◽  
Gravitational Potential ◽  
Galactic Center ◽  
Critical Mass ◽  
Time Dependent ◽  
Fermion Mass ◽  
Massive Black Hole ◽  
Sgr A

The motion of S-stars around the Galactic center implies that the central gravitational potential is dominated by a compact source, Sagittarius A* (Sgr A*), which has a mass of about 4 × 106 M⊙ and is traditionally assumed to be a massive black hole (BH). The explanation of the multiyear accurate astrometric data of the S2 star around Sgr A*, including the relativistic redshift that has recently been verified, is particularly important for this hypothesis and for any alternative model. Another relevant object is G2, whose most recent observational data challenge the scenario of a massive BH: its post-pericenter radial velocity is lower than expected from a Keplerian orbit around the putative massive BH. This scenario has traditionally been reconciled by introducing a drag force on G2 by an accretion flow. As an alternative to the central BH scenario, we here demonstrate that the observed motion of both S2 and G2 is explained in terms of the dense core – diluted halo fermionic dark matter (DM) profile, obtained from the fully relativistic Ruffini-Argüelles-Rueda (RAR) model. It has previously been shown that for fermion masses 48−345 keV, the RAR-DM profile accurately fits the rotation curves of the Milky Way halo. We here show that the solely gravitational potential of such a DM profile for a fermion mass of 56 keV explains (1) all the available time-dependent data of the position (orbit) and line-of-sight radial velocity (redshift function z) of S2, (2) the combination of the special and general relativistic redshift measured for S2, (3) the currently available data on the orbit and z of G2, and (4) its post-pericenter passage deceleration without introducing a drag force. For both objects, we find that the RAR model fits the data better than the BH scenario: the mean of reduced chi-squares of the time-dependent orbit and z data are ⟨χ̄2⟩S2,RAR ≈ 3.1 and ⟨χ̄2⟩S2,BH ≈ 3.3 for S2 and ⟨χ̄2⟩G2,RAR ≈ 20 and ⟨χ̄2⟩G2,BH ≈ 41 for G2. The fit of the corresponding z data shows that while for S2 we find comparable fits, that is, χ̄2z,RAR ≈ 1.28 and χ̄2z,BH ≈ 1.04, for G2 the RAR model alone can produce an excellent fit of the data, that is, χ̄2z,RAR ≈ 1.0 and χ̄2z,BH ≈ 26. In addition, the critical mass for gravitational collapse of a degenerate 56 keV-fermion DM core into a BH is ∼ 108 M⊙. This result may provide the initial seed for the formation of the observed central supermassive BH in active galaxies, such as M 87.

scholarly journals 11.15. The effect of a central massive black hole on the gas fueling

1998 ◽  
Vol 184 ◽  
pp. 485-486
Author(s):  
H. Fukuda ◽  
A. Habe ◽  
K. Wada
Keyword(s):  
Black Hole ◽  
Numerical Simulations ◽  
Gravitational Potential ◽  
Galactic Center ◽  
The Self ◽  
Massive Black Hole ◽  
Nuclear Regions ◽  
Self Gravity ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance

Nuclear activities in galaxies, such as nuclear starbursts or AGNs, are supposed to be induced by gas fueling into nuclear regions of galaxies. Non-axisymmetric gravitational potential caused by a stellar bar is a convincing mechanism for triggering gas fueling (Phinney 1994). However, numerical simulations have shown that the bar can not force the gas to accrete toward the galactic center beyond the inner Lindblad resonance (ILR). As a mechanism to overcome the ILR barrier, the double barred structure (Friedli & Martinet 1993), or the self-gravity of gas (Wada & Habe 1992, 1995; Elmegreen 1994) are proposed.

Sculpting the central parsec of our Galaxy

2014 ◽  
Vol 10 (S312) ◽  
pp. 126-127
Author(s):  
Xian Chen
Keyword(s):  
Star Formation ◽  
Galactic Center ◽  
Stellar Dynamics ◽  
Stellar Disk ◽  
Red Giants ◽  
Massive Black Hole ◽  
Ob Stars ◽  
Star Forming ◽  
Sgr A ◽  
Central Parsec

AbstractRecent observations have revealed various structures within the gravitational influence of Sgr A* – the massive black hole in the Galactic center. These structures apparently defy the fundamental principles of star formation and stellar dynamics. On one hand, the red giants display a flat density profile, contrary to the cuspy one predicted by conventional stellar relaxation. On the other, Wolf-Rayet and OB stars are observed where in-situ star formation should have been prohibited by the strong tidal force from Sgr A*, and their spatial and phase-space distributions also contradict our understanding of stellar dynamics. To explain each of these inconsistencies, many scenarios have been proposed, which render the model increasingly complicated. Here, we suggest that the sub-parsec stellar disk surrounding Sgr A*, which was recently discovered, can reconcile all the above inconsistencies. We show that during the fragmenting past of this disk, the star-forming clumps could efficiently deplete red giants by repeatedly colliding with them. We also show that because of the torque exerted by the disk, stars within the central arcsec from Sgr A* would quickly mix in the angular-momentum space, which naturally explains the observed distributions of Wolf-Rayet and OB stars. Our results imply that Sgr A* was fueled by gas and stars several millions years ago and could have been an energetic AGN. We discuss future observations that can further testify our model.

scholarly journals Observing a black hole event horizon: (sub)millimeter VLBI of Sgr A*

2009 ◽  
Vol 5 (S261) ◽  
pp. 271-276 ◽  
Author(s):  
Vincent L. Fish ◽  
Sheperd S. Doeleman
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Evidence ◽  
Galactic Center ◽  
Strong Field ◽  
Variable Component ◽  
Massive Black Hole ◽  
Black Hole Candidate ◽  
Long Baseline ◽  
Sgr A

AbstractVery strong evidence suggests that Sagittarius A*, a compact radio source at the center of the Milky Way, marks the position of a super massive black hole. The proximity of Sgr A* in combination with its mass makes its apparent event horizon the largest of any black hole candidate in the universe and presents us with a unique opportunity to observe strong-field GR effects. Recent millimeter very long baseline interferometric observations of Sgr A* have demonstrated the existence of structures on scales comparable to the Schwarzschild radius. These observations already provide strong evidence in support of the existence of an event horizon. (Sub)Millimeter VLBI observations in the near future will combine the angular resolution necessary to identify the overall morphology of quiescent emission, such as an accretion disk or outflow, with a fine enough time resolution to detect possible periodicity in the variable component of emission. In the next few years, it may be possible to identify the spin of the black hole in Sgr A*, either by detecting the periodic signature of hot spots at the innermost stable circular orbit or parameter estimation in models of the quiescent emission. Longer term, a (sub)millimeter VLBI “Event Horizon Telescope” will be able to produce images of the Galactic center emission to the see the silhouette predicted by general relativistic lensing. These techniques are also applicable to the black hole in M87, where black hole spin may be key to understanding the jet-launching region.

scholarly journals OH in the Environment of Sgr A

1989 ◽  
Vol 136 ◽  
pp. 421-422
Author(s):  
Aa. Sandqvist ◽  
R. Karlsson ◽  
J. B. Whiteoak
Keyword(s):  
Radial Velocity ◽  
Shell Structure ◽  
Spiral Structure ◽  
Angular Resolution ◽  
Galactic Center ◽  
Absorption Lines ◽  
Molecular Gas ◽  
Center Region ◽  
Circumnuclear Disk ◽  
Sgr A

The 18-cm distribution of OH in the Galactic Center region near Sgr A has been mapped in all four of the 1612, 1665, 1667 and 1720 MHz OH absorption lines using the VLA with 4 arcsec angular resolution and 9 kms-1 velocity resolution. The OH gas at +50 and +20 kms-l is seen clearly in absorption against the shell structure of Sgr A East but not against the spiral structure of Sgr A West, possibly implying that this molecular gas lies between the two continuum components - behind Sgr A West and in front of Sgr A East. Inside the Circumnuclear Disk, there is a new neutral streamer which sweeps from the disk in towards Sgr A∗ as the observed radial velocity decreases from +78 to +16 kms-1. The streamer may have a negative-velocity counterpart on the opposite side of Sgr A∗.

scholarly journals The effect of dark matter on stars at the Galactic center: The paradox of youth problem

2020 ◽  
Vol 29 (08) ◽  
pp. 2050052
Author(s):  
Ebrahim Hassani ◽  
Reza Pazhouhesh ◽  
Hossein Ebadi
Keyword(s):  
Black Hole ◽  
Dark Matter ◽  
Galactic Center ◽  
Young Stars ◽  
Evolutionary Models ◽  
Massive Black Hole ◽  
Physical Conditions ◽  
Dm Effect ◽  
Evolutionary Paths ◽  
Evolutionary Simulations

Stars that evolve near the Galactic massive black hole show strange behaviors. The spectroscopic features of these stars show that they must be old. But their luminosities are much higher than the amounts that are predicted by the current stellar evolutionary models, which means that they must be active and young stars. In fact, this group of stars shows signatures of old and young stars, simultaneously. This is a paradox known as the “paradox of youth problem” (PYP). Some people tried to solve the PYP without supposing dark matter (DM) effects on stars. But, in this work, we implemented Weakly Interacting Massive Particles (WIMPs) annihilation as a new source of energy inside such stars. This implementation is logical for stars that evolve at high DM density environments. The new source of energy causes stars to follow different evolutionary paths on the H-R diagram in comparison with classical stellar evolutionary models. Increasing DM density in stellar evolutionary simulations causes the deviations from the standard H-R diagrams becomes more pronounced. By investigating the effects of WIMPs density on stellar structures and evolutions, we concluded that by considering DM effects on stars at the Galactic center, it is possible to solve the PYP. In addition to DM effect, complete solutions to PYP must consider all extreme and unique physical conditions that are present near the Galactic massive black hole.

scholarly journals Observations of the gas cloud G2 in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 254-263
Author(s):  
S. Gillessen ◽  
R. Genzel ◽  
T. K. Fritz ◽  
F. Eisenhauer ◽  
O. Pfuhl ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Accretion Rate ◽  
Tidal Effects ◽  
Massive Black Hole ◽  
Radial Orbit ◽  
Sgr A ◽  
The Many ◽  
Gas Cloud ◽  
Luminosity Evolution

AbstractIn 2011, we discovered a compact gas cloud (“G2”) with roughly three Earth masses that is falling on a near-radial orbit toward the massive black hole in the Galactic center. The orbit is well constrained and pericenter passage is predicted for early 2014. Our data beautifully show that G2 gets tidally sheared apart due to the massive black hole's force. During the next months, we expect that in addition to the tidal effects, hydrodynamics get important, when G2 collides with the hot ambient gas around Sgr A*. Simulations show that ultimately, the cloud's material might fall into the massive black hole. Predictions for the accretion rate and luminosity evolution, however, are very difficult due to the many unknowns. Nevertheless, this might be a unique opportunity in the next years to observe how gas feeds a massive black hole in a galactic nucleus.

scholarly journals The methods for searching hypervelocity star candidates from the SDSS

2013 ◽  
Vol 9 (S298) ◽  
pp. 421-421
Author(s):  
Yinbi Li ◽  
Ali Luo ◽  
Gang Zhao ◽  
Youjun Lu
Keyword(s):  
Black Hole ◽  
Velocity Distribution ◽  
Radial Velocity ◽  
Binary Stars ◽  
High Velocity ◽  
Main Sequence ◽  
Galactic Center ◽  
Main Sequence Stars ◽  
Massive Black Hole ◽  
Stellar Spectra

AbstractHyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this paper, we firstly select F and G type main sequence stars from about 370,000 stellar spectra of DR7. Then, we select 369 high velocity stars from main sequence samples using the radial velocity distribution. Finally, we find 13 possible unbound hyper-velocity star candidates from the 369 high velocity stars.

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